External power supplies for appliances are widely used to adapt an appliance easily to different power sockets by providing the appliance with a respective external power supply. External power supplies are also known as AC-adapter, plug-pack, power adapter or DC-Pack. Other reasons to use an external power supply are reduced size and costs of the appliance and for making an appliance for international sale with a variety of external power supplies.
Power line communication (PLC) is getting more and more popular as data transmission for Home Networking Technology. Power line communication is used e.g. for home devices like residential gateways or set-top boxes having an external power supply. Combining the external power supply with a power line communication modem into a single device has the advantage of reduced costs and reduced size of the appliance. A disadvantage of such a solution is that the power line modem is always on and consuming power, even when the appliance is switched off. Due to environmental reasons, there are therefore regulations in discussion for reducing power consumption in external power supplies. For example EU regulation No. 1275/2008 requires to reduce the standby energy consumption of consumer appliances below 1 Watt within the next years.
JP-A-2009-065265 discloses an office apparatus comprising an external power supply including a power line communication modem, which external power supply can be switched off and correspondingly the modem by means of a mains switch at the apparatus. A disadvantage is that a second power supply within the apparatus and a second power line to the apparatus are required. In another embodiment, the external power supply includes a current detection part detecting a current value flowing through the power line to the apparatus and the modem includes a microcontroller coupled to the current detection part for detecting when a power saving reset switch is pushed at the apparatus. The microcontroller recognizes also when the mains switch at the apparatus is switched off based on the current detection result of the current detection part, for reducing the power consumption of the apparatus.
EP-A-0804026 describes a separate box arranged between the mains supply and a consumer appliance, which box comprises a resistor as a current detector, a relay, a threshold detection circuit and an infrared detector, for switching off the mains voltage for the appliance with a delay, when the appliance is in a standby mode, and which switches on the mains voltage for the appliance in case signals of any remote control are received.